Running many child processes in parallel

class Runner : IDisposable {
  ConcurrentBag<Process> Processes = []
  ...
  void Execute() {
    ...
    Parallel.ForEach(items, item => {
      string Command = ...
      Processes.Add(Process.Start(Command));
    }
  }
  ...
  void Dispose() {
    foreach (var p in Processes) {
      // ?
    }
  }
}